JPH06507336A - Hybrid control method and system for flow control of liquid coating materials - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Hybrid control method and system for flow control of liquid coating materials Technical field The present invention relates to a method and system for controlling the flow rate of liquid coating materials, and more particularly to methods and systems for controlling the flow rate of liquid coating materials. Specifically, by controlling the flow regulator in response to a reference signal. ,liquid! ! ! Hybrid fI4 control method and system for controlling the flow rate of packaging materials related.

Technical background In full-time closed-loop fluid control systems, the desired flow rate is compared to the actual flow rate. control algorithms that often include gain factors to achieve the desired flow rate. The output command signal is corrected based on the output command signal. This kind of closed loop system is commonly In order to bring the actual flow rate in the line to the commanded flow rate, periodic basis It will be activated later.

One problem associated with this type of full-time closed loop system is that this type of control method It is said that the method does not perform well in systems that exhibit poor dynamic response characteristics. That is. In this type of closed-loop system, this ensures the stability of the system. This is because the gain is set extremely low in order to maintain such low gain Under these conditions, the f14ml system takes an extremely long time to reach the desired set point. This will end up taking a lot of time.

Another method often used in fluid control systems is the open-loop method, In this method, calibration data correlates a given output command with the actual flow rate. I get kicked. In this type of system, the output command (jl, flow set point) manually set and then continuously perform the operation to check the flow rate for a given period It is necessary to perform the calibration by iteration. This operation The command is run until the desired flow rate is achieved. In this kind of open loop is used when the range of flow rates to be controlled is wide and the system is nonlinear. Typically, multiple calibration points are required.

One of the key issues with this overarching open-loop control system is that the accuracy of the calibration data This means that it is only as accurate as a dynamically calculated data value. due to human error This can result in bad data and, depending on how often the process is modified, the calibration process A large amount of fluid may be wasted during the process.

In addition, it is important for the process to turn off the lines of the open-loop system (inside the piping) during calibration. flow (stoppage), and this period corresponds to lost production time.

Additionally, this type of open-loop fluid control system directly affects fluid viscosity, resulting in does not automatically adapt to changes in fluid temperature that affect fluid flow rate. considerable temperature If there is a change, the manual calibration procedure for accurate fluid flow control must be This means that it needs to be repeated at a certain temperature.

A further interlayer in this type of open loop fluidic fRII system is The system must not be too focused on system hysteresis. In other words, the system to achieve a predetermined flow rate when the is operating at a flow rate lower than the predetermined flow rate. The output or reference command required for required to achieve the same predetermined flow rate as in the previous case when operating at may be different from the standard output command.

A number of other problems associated with both types of fluid control systems include: (1) Automatically adjust system gains for each fluid used; (2) calibrating the flow meter based on temperature changes or (3) lack of setpoint variability with humidity fluctuations; (4) ability to account for differences in system response time based on command direction; lack, etc.

U.S. Patent No. 4,724°865 to Hirano et al. A control circuit for a pressure fluid control valve is disclosed. This control circuit controls the error signal to a predetermined level. If the front side is set from closed-loop control based on the error signal, Control loop switcher that switches the control mode (to open loop control) based on the input signal It has a structure.

U.S. Patent 4.787°332, granted to Gelsel et al. An adhesive dispensing pump control system is disclosed for use in The flow rate of adhesive material applied to the workpiece is automatically varied.

In this system, the pressure difference between the inlet and outlet of the dispensing pump is substantially reduced. By holding it constant, the system is protected against changes in the viscosity of the adhesive being applied. Make the system's sensitivity relatively dull.

U.S. Pat. No. 4,679.585, issued to Mr. Ewiog, includes a electric to enhance the response and offset the hysteresis of the valve armature suspension. A fast response flow meter is disclosed that develops an electrical circuit that induces mechanical vibrations.

U.S. Patent 4,838.311, granted to Mr. Vetter, includes a painting robot. A programmed spray installed is disclosed for the control system for the device. Ru.

Pilot automatically controlled as a function of the relative position of the robot and the car body to be painted. The needle valve allows the paint to switch on and off at predetermined times. and switched off.

U.S. Pat. No. 4,705°083, issued to Mr. Rossetti, describes the By calculating the delay time for opening and closing the valve, the colorant Calibrates the amount of colorant released from the solenoid valve to be applied with an error of less than -cent A computerized method for doing so is disclosed.

U.S. Patent No. 4.726°528, granted to Mr. Galotto, states that Pressure to sense the pressure of supplying enamel or paint to the attached spray gun A pressure equalizer having a force sensing element and for use with a robot is disclosed. Ru.

Patent No. 3.653 is a U.S. patent that has some relevance to the present invention. , No. 393, No. 3.989゜935, No. 4.162.689, No. 4.420 , No. 812, No. 4.484.120, No. 4,546.795, No. 4.556 ．． 032, 4.785.760, and Higashi 4.807.561. It will be done.

Disclosure of invention The object of the invention is to initially control the flow regulator in open loop mode, Then close the flow regulator after the fluid flow rate through the regulator has stabilized. The object of the present invention is to provide an improved method and system for controlling in loop mode. .

Another object of the invention is that the initial command used in open loop mode is The calibration data is determined from the actual flow rate required to achieve the desired flow rate. Controls a flow regulator configured to update based on the commands of The object of the present invention is to provide an improved method and system for doing so.

Yet another object of the invention is to use the system in open loop mode. Calibration data is collected and stored for a particular fluid, in which case the calibration data such as fluid temperature, fluid viscosity, and mechanical/pneumatic system changes. configured to be dynamically updated to compensate for fluctuations in system operating conditions. The objective is to provide an improved method and system. This makes the calibration data , automatically between the blades to achieve the desired flow rate.

In achieving the foregoing and other objects of the present invention, a flow regulator and a transformer for operating the flow regulator in response to electrical control signals. A method is provided for controlling a user. regulated by flow regulator The flow rate of liquid coating material is controlled in response to a reference signal. This method is , has a closed-loop mode and an open-loop mode. This method uses liquid painting materials storing a calibration data set representing at least one expected flow rate for including. Furthermore, the method generates the configuration signal as a function of the reference signal. a step of associating a reference signal with calibration data for The flow regulator adjusts the flow rate of the liquid coating material to the expected flow rate. The method includes the step of generating a first electrical control signal according to the setting signal. This person The method further generates a feedback signal as a function of the adjusted liquid coating material. step and the error as a function of the difference between the set-up signal and the feedback signal. and generating a signal. Furthermore, in closed-loop mode, the function of the error signal is The step of generating an electrical control signal of W12 as a number is included. The error signal is Represents the desired amount of change in flow rate of liquid coating material. Finally, a first electrical control signal is generated. After a predetermined period of time has elapsed after the step Can be changed to closed loop mode. Furthermore, this method is useful in practice in closed-loop mode. If the flow rate is within the predetermined flow range represented by the second electrical control signal, A set of modified calibration data representing desired flow rates to compensate for variations in system operating conditions. Preferably, the method includes the step of modifying the settings of the data.

Additionally, this method allows spray painting of objects placed within the painting zone. In this case, the method uses a support head that is movable around multiple control axes. Use a robot equipped with An atomization device is attached to the support head. centre A low regulator controls the flow of liquid coating material from the liquid supply source to the atomizer. control Spraying is a method of painting in which an atomized liquid coating material is applied to the surface of an article. The atomizer is moved around multiple control axes to spray objects in the coating zone. to various positions along a programmed path located at predetermined distances from The moving steps and spraying of objects within the coating zone are performed to control the coating. Each of the above, including the step of automatically and cooperatively operating the flow regulator and the robot. Has steps.

In order to achieve the foregoing and other objects of the present invention, a system for carrying out each of the foregoing methods is provided. A stem is also provided.

Additionally, the temperature is measured to generate a temperature signal as a function of the temperature of the conditioned liquid coating material. Preferably, a temperature sensor is used, which temperature signal is determined as a function of the temperature signal. It may also be used to modify the calibration data settings.Similarly, the humidity sensor can be It may be used in almost the same manner as the degree sensor.

By using the method and system of the present invention, many’! 31. a is brought about.

For example, manual work, material waste, and production time losses can be significantly reduced. Ru. Furthermore, the method and system of the present invention provides, in a preferred 111 embodiment of the present invention, Easy to use for robotically operated spray equipment as described Applicable to

The present invention may be better understood by reference to the following detailed description in conjunction with the accompanying drawings. Once understood, the advantages of the present invention can be easily appreciated.

Brief description of the drawing FIG. 1 is a schematic diagram illustrating the method and system of the present invention.

FIG. 2 is a schematic diagram illustrating the controller of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Referring to the figures, various embodiments of the present invention for painting parts, such as automobile parts, are shown. A paint spray control method and system is presented that incorporates such features.

A paint spray system typically includes an atomizing device, such as a spray gun 10. I'm reading. This spray gun 10 is a support for an arm 14 that is a part of a robot 16. Preferably, it is attached to the port head 12. Robot 16 is a program It is a multi-ring spray gun with a rammed movement and is usually an assignee of Honreihe. It can be obtained by purchasing from. The spray gun is SA It is available from MES.

Although the preferred embodiment of the invention utilizes a robot 16, the method and system The stem is suitable for manual or automated systems as well as robotic systems. It should also be understood that it is possible to use

The spray gun 10 generally contains the paint in which a part or article is to be painted. It is attached to the support head 12 within the spray booth. The part concerned is a paint sprayer. It is often carried through the painting zone within the Ray booth.

The robot 16 is controlled by a programmable control means or controller 24. controlled by Under the control of the robot controller 24, the robot 16 , thus the spray head 12 is located within the painting zone of the paint play booth. at various locations along a programmed path a predetermined distance from the item. The atomizing device 10 can be moved around a plurality of control axes until it reaches the desired position.

The pneumatic spray gun 10 supplies paint from a paint or liquid source 28. It has a liquid paint passageway (not shown) in fluid communication with supply line 26. liquid supply Source 28 can be in the form of either a paint pressure tank or a paint recirculation line. I can't support it. The paint is supplied in a controlled manner by a controlled flow regulator 30. and is supplied to the paint supply line 26. The flow regulator is from SAMES. Available with manifold integral with paint regulator It is preferable.

On the other hand, the flow regulator 30 is connected to the converter means or transducer 32. Controlled by air control signals from. This type of transducer is Prop available from Ortion Air Company.

The pneumatic control signal generated by transducer 32 is transmitted to a control system or Under the control of a fluid flow controller designated throughout this specification by the reference numeral 34. is generated from a pressurized air source or source. Liquid supply source 28 supplies paint pressure. In the case of a power tank, the air supply source also supplies air pressure to the liquid supply 1&l [28]. It's okay to do that. If the atomization device is a pneumatic spray gun, the air supply The source is also fluidly connected to an atomizing air passageway (not shown) of the spray gun 10. It's okay to stay.

Control system 34 controls flow regulator 30 via transducer 32. Hybrid control system with open-loop mode and closed-loop mode to control It is characterized by being a stem. Under the control of the control system 34, regulator 30 receives a reference from robot controller 24 that appears on line 38. In response to lens signal *A, the flow rate of liquid coating material is adjusted.

In calibration mode, calibration data is transmitted by a feedback means or mechanism. determined offline.

The feedback mechanism uses a regulated liquid dispenser to obtain an electrical flow signal. A flow transducer that supplies frequency No. 1*F to measure the actual flow rate of the packaging material. Preferably, a sensor or sensor 40 is included. The flow signal consists of many pulses. and the number of these pulses is such that the regulated liquid coating material passes through the regulator 30. is a function of the actual flow rate. Sensor 40 is available from Kupper, Inc. Also called gear meter.

The feedback mechanism counts the number of noggles included in the flow signal. a counter means or counter within the control system 34; . The count in the counter indicates the amount of regulated liquid coating material passing through regulator 30. Represents the actual flow rate.

Mode control switches 44 and 46 are connected to switch 48 by serial communication line 48. a keyboard coupled to the system 34 or I10 interface 42 coupled to the (not shown). The I10 interface 42 A programmable logic controller may also be provided.

The signal from I10 interface 42 is in the top position of switches 44 and 46. When used, it is coupled directly to transducer 32 in transparent mode.

When switches 44 and 46 are in the second horizontal position, system 34 is open-route. mode.

Finally, when switches 44 and 46 are in the third lowest position, system 34 enters closed-loop adaptation mode.

However, as shown in block 50, there is a change in the set signal by more than a predetermined amount. In some cases, system 34 may enter open loop mode from closed loop mode. can.

In calibration mode, the user-selected operating range for the user-selected fluid is All calibration data is then entered into the calibration data table 52. In general, users The sample points that can be selected are electrical signals within the range of 4mA to 20mA. is scaled by a scaling unit 53 that takes in the engineering unit and converts it into engineering units. entered in engineering units. This data is available for later use. an interpolation unit that calculates the initial (i.e. in open loop) flow command in order to 54 for calculation of slope and Y-intercept tables.

Robot controller 24 typically performs calibration via I10 interface 42. Start the cycle. However, the calibration cycle can be performed in situ, e.g. may be initiated locally in the control system 34, as well as I want you to understand.

Additionally, the calibration data is typically stored in a storage device, such as a semiconductor storage device, in tabular form. I also want you to understand that I will be remembered for this. Calibration data is limited for liquid coating materials. represents at least one expected flow rate.

In open-loop mode (i.e., there are typically relatively large changes in the input signal) ), the block Enter 57. In block 57, a delay period is set and the flow point is The system remains in open-loop mode for a limited period of time to allow the system to stabilize. child The amount of time is set during calibration to ensure system response time and the full range of input signals. depends on the amount of change in the input signal over the surrounding area. Table 52 provides information regarding each paint type or color. It is preferable to have one set of points (for example 10 points) over the usable flow rate range. stomach.

Interpolation unit 54 must allow set values to be set between the points in table 52. Must be. Preferably, the interpolation unit 54 uses a linear interpolation method.

As previously mentioned, the flow sensor 40 controls the flow of liquid through the flow regulator 30. Measures the flow rate of the packaging material and outputs a flow rate signal. In this case, the frequency of flow rate No. 1 is Represents the flow rate through flow regulator 30.

The robot controller 24 sends flow commands or The I10 interface 42 transmits the reference signal to the line 38. to the control system. In this case, the magnitude of each flow command signal is Directly proportional to desired flow rate. Generally, when control system 34 receives a new command signal, then calculates an initial or open-loop flow command by interpolation unit 54. For this purpose, access to appropriate calibration data is made. Initial open loop flow command A signal appears on line 56, the first electrical control signal being in open loop mode. It is output at switch 46. The first electrical control signal is along line 58. and sent to the transducer 32. The transducer 32 then receives the control signal is converted into a signal for controlling the flow regulator 30, and as a result, the flow rate is The regulator will supply liquid at the scheduled flow rate according to the calibration data contained within Table 52. The flow rate of liquid coating material flowing from the source to the atomization device 10 is adjusted.

The sensor reward 62 receives the feed generated by the flow sensors 40 and 42. Compare the back signal and setpoint signal. In other words, the junk 1 pin 62 is Compare the actual flow rate with the selected setpoint.

If the change in flow rate is less than the scheduled amount (i.e. 2%), is the delay period zero? The correction delay is tested at block 64 to determine whether the correction delay is corrected or not. at zero If not, it will not be changed. If the delay period is zero, the correction algorithm blocks is input into the block 66.

The correction algorithm 66 implements the PI method. In this case, the new output value is the set value The conventional output value is the value obtained by multiplying the difference between the actual flow rate and the gain coefficient by the integral term. Equal to the added value (i.e., new output value, old output value + gain (set value - actual [1 + I ).

Block 68 determines whether the error is greater or less than a predetermined tolerance. , the actual flow rate and the correct flow rate! ! (i.e., error) is tested.

If the error is greater than the tolerance, then in block 70 the output command (immediately (i.e., a second electrical control signal) is output on line 58 via switch 46.

In block 70, the digital value of the output signal is converted into an analog representation (4 to 20 mA range).

If the error signal is less than the tolerance specified above, the calibration table correction table loop is blocked. Lock 72 is entered. Is the error within the expected shift band for a particular calibration point? The error is tested at block 72 to see if the error is correct.

If so, block 74 is immediately entered where the calibration table is updated. be renewed. In this way, a particular calibration point is corrected.

However, if the error is outside the predetermined shift band, block 76 Interpolation is performed in block 78 and the entire table of points is It is "tilted" around the origin of the table. In general, the higher the flow rate, the more The positive value is also large. In addition, the robot controller 24 has a humidity sensor. For example, when will a new flow set point be reached?

Finally, the flow sensor 40, whether digital or analog in nature, , any type of flow feedback signal may be provided.

Accordingly, without being limited by the detailed description, the invention resides in the claims appended hereto. It is to be understood that implementation is possible within the scope.

('J Copy and translation of written amendment) Submission form (Article 184-7, Paragraph 1 of the Patent Act) April 28, 1993

Claims (18)

[Claims] 1. a flow regulator; and a flow regulator in response to a reference signal. responsive to an electrical control signal for controlling the flow rate of the liquid coating material regulated by the and a transducer for operating the flow regulator. In the method, the method has a closed-loop mode and an open-loop mode; storing a calibration data set representing at least one expected flow rate for the body coating material; a reference signal to generate a set signal as a function of the reference signal; associating a lens signal with the calibration data; the flow regulator adjusting the flow rate of liquid coating material to the expected flow rate; , generating a first electrical control signal according to the setting signal in open loop mode; Steps to follow: Generates a feedback signal as a function of the actual flow rate of the regulated liquid coating material. determining an error as a function of the difference between the set signal and the feedback signal; generating a difference signal; said error signal representing a desired change in liquid coating material flow rate; the second electrical control signal as a function of the error signal in closed-loop mode, after the step of generating the first electrical control signal; and then switch from open-loop mode to closed-loop mode after a predetermined period of time. and switching. 2. a predetermined flow rate, the actual flow rate being represented by the second electrical control signal; Desired flow rate to compensate for varying system operating conditions when within the specified range Modify said calibration data set to obtain a modified calibration data set representing 2. The method of claim 1, further comprising the step of correcting. 3. Generating a temperature signal as a function of the temperature of the conditioned liquid coating material 3. The method of claim 2, further comprising . 4. Robot with arms with support heads movable around multiple control axes an atomizing device attached to the support head; and an atomizing device attached to the support head; Flow regulator and reference to control the flow rate of liquid coating material to the coating equipment. a flow of liquid coating material regulated by the flow regulator in response to an action signal; operating the flow regulator in response to an electrical control signal to control the amount; spray paint items within the painting zone using a transducer for , the method has a closed-loop mode and an open-loop mode. Along with; Store a calibration data set representing at least one expected flow rate for the liquid coating material. the steps of: generating a set signal as a function of the reference signal; associating the reference signal with calibration data; the flow regulator adjusting the flow rate of liquid coating material to the expected flow rate; a step for generating a first electrical control signal according to a set signal in an open loop mode; and ; Generating a feedback signal as a function of the actual flow rate of the regulated liquid coating material determining an error as a function of the difference between the set signal and the feedback signal; generating a difference signal; the error signal representing a desired change in liquid coating material flow rate; the second electrical control signal as a function of the error signal in closed-loop mode when after the step of generating the first electrical control signal; to switch from open-loop mode to closed-loop mode after a predetermined period of time. spraying the surface of the article with the atomized liquid coating material; The atomizer is moved around multiple control axes at a predetermined distance from the article in the coating zone. moving to various positions along the programmed path located at; said flow regulator for controlling spray coating of articles within said coating zone; automatically operating the robot in a coordinated manner; The method comprising: 5. a predetermined flow rate whose actual flow rate is represented by said second electrical control signal; Desired flow rate to compensate for varying system operating conditions when within the specified range Modify said calibration data set to obtain a modified calibration data set representing 5. The method of claim 4, further comprising the step of correcting. 6. Generating a temperature signal as a function of the temperature of the conditioned liquid coating material 6. The method of claim 5, further comprising . 7. Controls the atomizer and the flow of liquid coating material from the liquid source to the atomizer a flow regulator for A flow regulator is used to control the flow rate of liquid coating material regulated by a a control system having an open loop mode and a closed loop mode for controlling the A system for spray painting articles in a painting zone, the control system comprising: Tim is Store a calibration data set representing at least one expected flow rate for the liquid coating material. storage means for obtaining the set signal as a function of the reference signal; means for associating the reference signal with calibration data; The flow regulator controls the flow of liquid from the liquid coating material supply to the atomization device. said setting in open loop mode to adjust body coating material flow rate to said expected flow rate. first means for generating the first electrical control signal in accordance with a constant signal; Generates a feedback signal as a function of the actual flow rate of the regulated liquid coating material. feedback means for; a difference between the setting signal and the feedback signal; generating means for generating an error signal as a function of the liquid coating material; When representing the desired change in flow rate, the error signal is expressed as a function of the error signal in closed loop mode. second means for generating a second electrical control signal; regulating the electrical control signal to operate the flow regulator as a function; A controller applied that can be coupled to a flow regulator for the purpose of converting it into a flow regulator control signal. With barter means; After a predetermined period of time has elapsed after the first electrical control signal was generated. mode control means for switching from open-loop mode to closed-loop mode at The system for spray painting. 8. a predetermined flow rate whose actual flow rate is represented by said second electrical control signal; Desired flow rate to compensate for varying system operating conditions when within the specified range said feedback means to obtain a modified calibration data set representing 8. The control according to claim 7, further comprising modification means for modifying the calibration data set. system. 9. Temperature control for emitting a temperature signal as a function of the temperature of the regulated liquid coating material. 9. The control system according to claim 8, further comprising a sensor. 10. Measure the actual flow rate of the regulated liquid coating material to obtain the flow signal Claim 7 further comprising feedback means having a flow rate transducer for Control system as described. 11. The implementation of liquid coating materials where the flow signal contains a large number of pulses and the number of pulses is adjusted. It is a function of the flow rate at which the feedbank means is used to count the number of pulses. 11. The control system according to claim 10, further comprising counter means. 12. said generating means generates an error signal as a function of the type of liquid coating material; The control system is coupled to a generating means for indicating the type of liquid coating material for spray coating. 8. The control system of claim 7, further comprising indicator means. 13. Prog with arms with support heads movable around multiple control axes a ram-controlled robot; an atomization device attached to said arm; and a liquid supply. Flow regulator to control the flow rate of liquid coating material from the source to the atomization device forward to various positions along a programmed path around multiple control axes. a robot controller for moving the device by the support head of the recording arm; The liquid application is regulated by the flow regulator in response to the reference signal. an open loop motor to control the flow regulator for controlling the flow rate of the packaging material; spraying objects in the painting zone with a control system that has a closed-loop mode and In the robot spray painting system for applying coating, the control system has a calibration data set representing at least one expected flow rate for the liquid coating material. storage means for storing; for generating the set signal as a function of the reference signal; means for associating a reference signal with the calibration data; The flow regulator controls liquid coating from the liquid coating material source to the atomization device. According to the set signal in open loop mode to adjust the material flow rate to the expected flow rate a first means for generating the first electrical control signal; and a controlled liquid coating material. Feedback to generate a feedback signal as a function of the actual flow rate of the material means; an error signal as a function of the difference between said setting signal and said feedback signal; generating means for generating; said error signal representing a desired change in liquid coating material flow rate; a second electrical control signal as a function of the error signal in closed loop mode when second means for generating; said flow regulation as a function of an electrical control signal; For the purpose of converting electrical control signals into regulator control signals to operate the motor. converter means coupledly adapted to said flow regulator; said flow regulator for controlling spray coating of articles within said coating zone; a first electrical control signal is generated to automatically coordinate the operation of the computer and the robot; later, from open-loop mode to closed-loop mode after a predetermined period of time. and mode control means for switching the robotic spray painting system. . 14. the actual flow rate is the predetermined flow rate represented by the second electrical control signal; desired flow to compensate for varying system operating conditions when within a specified range. said feedback means for obtaining a modified calibration data set representative of the quantity; as claimed in claim 13, wherein the calibration data set includes modification means for modifying the calibration data set. On-board control system. 15. temperature for generating a temperature signal as a function of the temperature of the regulated liquid coating material; 15. The control system of claim 14, further comprising a sensor. 16. the liquid coating, wherein the feedback means is regulated to obtain a flow rate signal; Claim 13 including a flow transducer for measuring the actual flow rate of the material. Control system described in. 17. The implementation of liquid coating materials where the flow signal contains a large number of pulses and the number of pulses is adjusted. The feedback means counts the number of pulses. 17. The control system of claim 16, further comprising counter means for. 18. said generating means generates an error signal as a function of the type of liquid coating material; The control system generates the generated hand for indicating the type of liquid coating material for spray coating. 14. The control system of claim 13, further comprising indicator means coupled to the stage. .